The present invention relates generally to fluid flow control valves and specifically to rotary fluid control valves of the type where a valve plug and a valve seat are brought into a fluid tight sealing engagement through an eccentric swinging movement of the valve plug.
Many different forms of rotary valves of the type identified above are known in the art. Such valves are also referred to as cam ball valves and eccentric ball valves and the terms are used interchangeably herein. One very popular valve of this type has a rigid seat with the plug semi-flexibly mounted, either through a flexible actuating arm, or through a flexible connection, between the plug and a rigid actuating arm. An example of such a rotary fluid control valve with a rigid seat and flexible actuating arm is found in U.S. Pat. No. 3,623,696. Most rotary valves with rigid seats have provision for adjusting tne seat in the housing to obtain the desired sealing engagement between the plug and the seat.
U.S. Pat. No. 4,118,008 shows a rotary cam ball valve with a rockable seat having tapered external walls which cooperate with corresponding tapered surfaces in the valve body for permitting angular displacement of the seat in response to forces exerted by the plug.
U.S. Pat. No. 4,215,846 shows an eccentric rotary valve in which the seat has support lips which are designed to flex when loaded by the valve plug. According to the patent, the forces are such that the flexing causes the lips to converge and form a tighter seal with the valve plug.
Although these various types of valves, valve seats and plug arrangements have no doubt found utility in many different applications, they all exhibit one or more shortcomings which have prevented any particular one of the valves from being entirely suitable in a variety of different operating environments.
The desirable characteristics for a rotary fluid control valve include tight shut-off, suitability for use in high pressure flow lines, ability of the design to withstand use with corrosive and erosive fluids, operational ease to minimize actuator loading, durability, especially resistance to wear in the seat and plug seal areas, and low manufacturing and assembly cost. The valves of the prior art meet many of these criteria. Those employing heavy rigid seats have excellent resistance to corrosion and physical damage to the seat, but are generally difficult to adjust for tight shut-off because they do not accommodate irregularities or misalignment between the seat and valve plug. On the other hand, valve designs incorporating thin metal seals or seats accommodate irregularities and misalignment in an effort to provide tight shut-off, but are very susceptible to corrosion and erosion damage. Further, many of the prior art valve designs are not suitable for use in high pressure flow lines.
Rotary cam ball valves inherently experience a great deal of wear on bearings, plugs and seats because of the wiping action and generally high forces experienced during opening and closing. As is well known, high bearing loading can lead to "galling" of the valve shaft and failure of the valve. Prior art rotary valves experience high load forces on their shafts and bearings when the valves are closed which detracts from their ability to operate in high pressure flowpaths. To say it another way, a rotary valve having lower friction during closure, can be used in a higher pressure drop line. Similarly, while such valves are operable in bidirectional flowpaths, the bearing loads and plug and seat friction forces differ substantially depending on whether the high pressure is applied to the front or rear of the plug. Thus it is difficult to optimize the design of a bidirectional rotary cam ball fluid control valve. Consequently, there is a need in the art for a rotary eccentric valve which is capable of satisfying the above criteria.